Spinal Epidural Abscess

Close to 90% of back pain related complaints in the ED are due to benign aetiologies. Only a limited number of patients have catastrophic diseases demanding immediate intervention. The process of ascertaining patients with grave diseases from the vast majority of patients with uncomplicated back pain can be tough. Therefore, a good history which identifies risk factors, a focussed back examination are paramount to pick any serious pathology.

Things that we should not be missing:

• AAA, Retroperitoneal Bleed, Epidural Hematoma
• Pyelonephritis, Psoas Abscess
• Cord Compression (due to a Central Massive Disc Herniation, Spinal Epidural Abscess or Bony Metastasis)
• Vertebral Fractures, Osteomyelitis
• Cauda Equina Syndrome (CES)

Note - Cord Compression is a UMN lesion (Hyperreflexia) and CES is an LMN lesion (Hypo/Areflexia). 

I am going to mention specifically about Spinal Epidural Abscess in this post.

Risk Factors for Spinal Epidural Abscess (SEA) 

Document these in the patients medical record.

• DM, HIV, Steroids, Renal Failure/ Hemodialysis, IVDU
• Trauma, Sx, Instrumentation of spine
• Recent Infections with bacteremia such as UTI, Respiratory infections, Bone, Skin or soft tissue infection

ED Presentation of Spinal Epidural Abscess

Classic triad of SEA is rare - Triad of Fever (seen only in < 50%), Pain, Neuro deficits  is seen only in 10-15% of patients. Insidious onset pain which gets worse at night and on recumbent position should ring the bells and should make us think about Infectious or cancer related pain. About 1/5th of the patients have no risk factors at all. 

Critical Exam Findings:

• Midline Spine Tenderness on percussion (Infection, Fracture)
• Saddle Anesthesia, Poor Rectal tone and peri-anal sensations (likely Cauda Equina)
• Fever (Spinal Infection)
• B/L multiple neurological deficits (likely Cauda Equina)
• Hyperreflexia (Suggests UMN lesion - Cord Compression)
• Hyporeflexia (Makes CES likely)

Caudal Equina Syndrome - Anything that compresses the lumbar spinal nerves at the lower end of the spinal cord can progress to cauda equine syndrome, leading to severe back pain, bowel/bladder dysfunction, sexual dysfunction, progression of neuro deficits, saddle anaesthesia and loss of rectal tone. Caudal equina can also present as gradual onset long standing pain. 

Document the findings of a focussed sensory-motor examination and gait, rectal exam findings. 

Myotomes 

Dermatomes

Diagnostic Pearls for Spinal Epidural Abscess

• Some consider multiple ED visits (without a diagnosis) as a red flag for Epidural Abscess and also new thoracic location pain. Patients may not always have midline tenderness but paraspinal tenderness. 
• Neuro dysfunction is rare in the beginning. It usually starts as motor —> sensory—> bowel and bladder dysfunction. We often get a false sense of reassurance in the absence of neurological deficits. 
• Inflammatory markers such as CRP is 90% sensitive but it is much better than WCC. (A negative CRP makes SEA unlikely but it can be non-specific). A normal WCC cannot rule out SEA. Anti-inflammatory medications such as steroids may also falsely lower the CRP. But still, always order a WCC (because high WCC is concerning), CRP and ESR for concerning back pain.
• X rays and CTs of spine do not reveal infectious etiologies. Use MRI to scan the entire spine with contrast because lesions often occur at multiple levels. When inflammatory markers are raised and the patient looks sick, administer broad spectrum Abx with MRSA and Gram negative cover.
• CT can be negative as well - it will again not show infectious causes of back pain, MRI is the test of choice. CT shows only bony lesions.

Who needs emergency MRI?

When evaluating back pain, order an emergency MRI if:

• Suspected spinal infection (fever, raised ESR or other risk factors for SEA) 
• Cord compression (progressive neuro deficits, hyperreflexia, h/o cancer, bony lesions on X-Ray). 
• Suspected Cauda Equine Syndrome (severe back pain, hyporeflexia, bowel/bladder/sexual dysfunction, saddle anaesthesia, paralysis)

Note: Isolated sensory findings or areflexia are not considered to be a progressive neurologic deficits.

Take Home: 

• Document the risk factors in patient's chart.
• Do a focused History and physical exam, rectal exam and gait assessment.
• When discharging these patients as MSK back pain,  give them verbal and written advice explaining the red flags and when to return back. 

Author:

              

     Lakshay Chanana

     

     Speciality Doctor

     Northwick Park Hospital

     Department of Emergency Medicine

     England

     @EMDidactic